Preparation of aqueous solutions of copolymers of dicarboxylic acids having a low dicarboxylic acid monomer content

Abstract

Very small amounts of certain metal ions promote copolymerization of aliphalic dicarboxylic acids with alpha , beta -ethylentically unsaturated monomers in an aqueous solution system maintained at a given pH range, whereby the amount of unreacted dicarboxylic acid monomer is significantly reduced while control of molecular weight of the resulting compolymers is maintained.

I claim: 
     
       1. In the process for the manufacture of water-soluble copolymers of a monoethylenically unsaturated dicarboxylic acid having from 4 to 6 carbon atoms and an α,β-ethylenically unsaturated monomer, said copolymers having a weight average molecular weight of from about 2,000 to about 1,000,000, in which said dicarboxylic acid which is at least partially neutralized is reacted with an α,β-ethylenically unsaturated monomer selected from the group consisting of (a) a monocarboxylic acid having from 3 to 10 carbon atoms and the alkali metal and ammonium salts thereof, (b) an organic sulfonic acid compound and the alkali metal and ammonium salts thereof, and (c) a vinyl monomer free of carboxyl and sulfonic acid groups, and mixtures of said (a), (b) and (c) monomers, at an elevated temperature in an aqueous polymerization system substantially free of an organic chain transfer agent, and in which said dicarboxylic acid is first dissolved in said aqueous polymerization system and is at least partially neutralized, and said α,β-ethylenically unsaturated monomer or monomers and a water-soluble initiator are added to said aqueous polymerization system during a period of from 3 to 10 hours, the total amount of monomers employed in said reaction comprising at least about 30 percent, by weight, of said aqueous polymerization system, the improvement which comprises reacting from about 25 to about 55 percent by weight, based on total weight of monomers, of said dicarboxylic acid with from about 45 to about 75 percent of any of said monomers (a), (b), and (c), and mixtures thereof, and carrying out said polymerization reaction at a temperature of from about 80° to about 100° C. in the presence of from about 1 to about 250 ppm, of a metal ion selected from the group consisting of Zn ++ , Co +++ , Co ++ , Cu ++ , Mo ++ , Fe +++ , Fe ++ , Cr +++ , Ni ++ , Ce ++++  and Ce ++ , based on the total weight of the aqueous polymerization system, said concentration of said metal ions being increased proportionally with increase in the molar ratio of said dicarboxylic acid monomer to the total of said (a), (b) and/or (c) monomers, the pH of said polymerization system being maintained in the range of from about 2 to about 4 when the molar ratio of dicarboxylic acid monomer to other monomers is from about 1:4 to about 1:3, and from about 4 to about 6 when the molar ratio of dicarboxylic acid monomer to other monomers is from about 1:1.5 to about 1:1. 
     
     
       2. The process according to claim 1 in which the molar ratio of metal ion to initiator is in the range of from about 1:300 to 1:4000. PG,25 
     
     
       3. The process according to claim 1 in which said (b) monomer is selected from the group consisting of vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, vinyltoluenesulfonic acid and the alkali metal and ammonium salts thereof, and a compound of the formula ##STR3## wherein R 1 , R 2  and R 3  are selected from the group consisting of hydrogen and lower alkyl, R 4  is lower alkylene or alkyl substituted lower alkylene, and M is hydrogen, an alkali metal or ammonium ion. 
     
     
       4. The process according to claim 1 in which said (c) monomer is selected from the group consisting of vinyl acetate, allyl alcohol, acrylamide, N,N 1  -dimethylacrylamide, N-methylolacrylamide, N,N 1  -methylenebisacrylamide, vinyl crotonate, ethylene glycol diacrylate, tripropylene glycol diacrylate, diallylphthalate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, vinyl pyrrolidone and N-vinyl-N-methyl-acetamide. 
     
     
       5. The process according to claim 1 in which an aqueous solution of a mixture of said (a), (b) and (c) monomers is added to said aqueous solution system. 
     
     
       6. The process according to claim 1 in which said water-soluble initiator is selected from the group consisting of hydrogen peroxide, t-butylhydroperoxide, sodium, potassium and ammonium persulfate, and 2,2 1  -azobis(2-amidinopropane)hydrochloride, and is present in an amount of from about 0.5 to about 10 percent, said percentages being by weight based on the total weight of monomers used in the process. 
     
     
       7. The process according to claim 1 in which said dicarboxylic acid monomer is maleic acid, a monoalkali metal maleate or a monoammonium maleate. 
     
     
       8. The process according to claim 1 in which from about 1 to about 5 ppm of said metal ion is present in said aqueous solution system. 
     
     
       9. The process according to claim 6 in which said initiator comprises hydrogen peroxide.